This invention relates to a photoelectric pulsation type pulsimeter.
Various attempts have been made in the past in order to stabilize the pulsation display of a portable pulsimeter. Most of them relate to a processing method of counted values when the pulse rate per minute is counted from the period of the pulsation signal obtained from a pulsation detection circuit. As an example, a processing system called a "4-data selection movement system" will be hereby explained. The 4-data selection movement system is a system which removes two values from the maximum value of the four pulsation conversion data D.sub.max and one value from the minimum value D.sub.min and displays one remaining data D.sub.R or D.sub.N. A definite example is shown in FIG. 2. FIG. 2(A) shows the operation in the case where noise 201 exists intermittently in the output of the pulsation detection circuit. Symbols a, b, c, d, e and f in FIG. 2 represent the values converted to the pulse rate per minute from the average of the periods of two continuous pulsation signals. It can be understood from FIG. 2(B) that the display value D.sub.N is stable for the intermittent noises 201.
As described above, the prior art technique is effective for the intermittent noises, but are not effective for the continuous noise. FIG. 3(A) shows the operation when the continuous noise 301 exists. The output waveform of the pulsation detection circuit shown in FIG. 3(A) is exactly the same as that of FIG. 2(A) described above, but no effect at all is exhibited for the continuous noise 301. In accordance with such a method which eliminates the noise by data processing, the noise is also recognized as the pulsation signal and calculation-processed, which limits the stability and accuracy of the pulse rate display.
On the other hand, a LED or the like has been used conventionally as a light emission device of a pulsimeter for detecting the change of blood flow rate by use of optical means for counting and displaying a pulse rate. However, if a LED is turned on continuously during measurement, the consumed current becomes extremely great. Therefore, an attempt has been made to reduce the consumed current by continuously turning on the LED in a minimum light emission time in which light emission of the LED can be perceived as the change of the blood flow rate. The operation of this prior art device will be explained briefly with reference to a schematic structural view of a photoelectric pulsimeter shown in FIG. 8.
LED 111 is used as the light emission device, which continuously emits the rays of light from a light emission signal c from a CPU 118 through switching transistor 113. The intensity of the light is regulated by a current limiting resistor 112. The emitted infrared light impinges against a finger 114 of a subject, and the blood flow rate is converted to the level of reflected rays of light and transmitted to the light reception device 115. A phototransistor is used as this light reception device. Since the output of the phototransistor 115 generates a current in accordance with the intensity of the reflected rays, a resistor 116 generates a blood flow voltage a in accordance with the blood flow rate of the finger. This blood flow voltage a is amplified and shaped by an amplification circuit 117 and outputs the HPUL signal b which is in synchronism with the pulsation. The HPUL signal b is inputted to CPU 118, which calculates the pulse rate per unit time and the like from the input period of the HPUL signal and writes the date into a memory, not shown, or displays it. Reference numeral 119 represents a battery for supplying a current to each of the circuits described above.
If the battery is used as the power source of the pulsimeter for the measurement by use of the means described above, the internal resistance of the battery becomes high when the battery capacity drops or when the ambient temperature is low. In such a case, the power source voltage drops due to a voltage drop caused by the current flowing through the light emission device when it is turned on, and a spike pulse which is in synchronism with the turn-on of the light emission device, occurs in a waveform shaping circuit as the final output stage of the amplification circuit and is likely to overlap with the HPUL signal.
FIG. 9 shows the state described above. Under the normal state, the HPUL signal b is only the pulse signal which is in synchronism with the pulsation as shown in b-1. But if the spike pulse occurs for the reason described above, it overlaps on the HPUL signal as shown in b-2 and if CPU recognizes this spike pulse as the HPUL signal, it cannot calculate the pulsation correctly.